corruption after crash

[Guy McArthur]

After a recent power outage, my YDL 2.1 PowerMac 9500 is behaving oddly.
The kernel comes up in a prompt like
mon>
which seems to be some kind of kernel-level debugging shell.

Changing the boot options, I can get it to come up using the 2.2.19 
kernel, but then the video is in bizarre psychedelic colors like it is 
being dithered down, and of course the sound modules don't load.

Seems like maybe a disk corruption in the /boot partition?